Arthroscopic devices and methods

ABSTRACT

A medical device includes an elongated sleeve having a longitudinal axis, a proximal end and a distal end. A cutting member extends distally from the distal end of the elongated sleeve, and has sharp cutting edges. The cutting head is formed from a wear-resistant ceramic material, and a motor coupled to the proximal end of elongated sleeve rotate the cutting member. The cutter is engaged against bone and rotated to cut bone tissue without leaving any foreign particles in the site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/960,084, filed Dec. 4, 2015, now U.S. Pat. No. 9,585,675, whichclaims the benefit of provisional application 62/250,315, filed on Nov.3, 2015, and of provisional application 62/245,796, filed on Oct. 23,2015, the full disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to arthroscopic tissue cutting and removaldevices by which anatomical tissues may be cut and removed from a jointor other site. More specifically, this invention relates to instrumentsconfigured for cutting and removing bone or other hard tissue and havinga ceramic cutting member.

2. Description of the Background Art

In several surgical procedures including subacromial decompression,anterior cruciate ligament reconstruction involving notchplasty, andarthroscopic resection of the acromioclavicular joint, there is a needfor cutting and removal of bone and soft tissue. Currently, surgeons usearthroscopic shavers and burrs having rotational cutting surfaces toremove tissue for such procedures. A typical arthroscopic shaver or burrcomprises a metal cutting member carried at the distal end of a metalsleeve that rotates within an open-ended metal shaft. A suction pathwayfor removal of bone fragments or other tissues is provided through awindow proximal to the metal cutting member that communicates with alumen in the sleeve.

When metal shavers and burrs “wear” during a procedure, which occursvery rapidly when cutting bone, the wear can be accompanied by loss ofmicro-particles from fracture and particle release which occurs alongwith dulling due to metal deformation. In such surgical applications,even very small amounts of such foreign particles that are not recoveredfrom a treatment site can lead to detrimental effects on the patienthealth, with inflammation being typical. In some cases, the foreignparticles can result in joint failure due to osteolysis, a term used todefine inflammation due to presence of such foreign particles. A recentarticle describing such foreign particle induced inflammation isPedowitz, et al. (2013) Arthroscopic surgical tools: “A source of metalparticles and possible joint damage”, Arthroscopy—The Journal ofArthroscopic and Related Surgery, 29(9), 1559-1565. In addition tocausing inflammation, the presence of metal particles in a joint orother treatment site can cause serious problems for future MRIs.Typically, the MRI images will be blurred by agitation of the metalparticles caused by the magnetic field used in the imaging, makingassessments of the treatment difficult.

Another problem with the currently available metal shavers/burrs relatesto manufacturing limitations in combination with the rapid dulling ofmetal cutting edges. Typically, a metal cutter is manufactured bymachining the cutting surfaces and flutes into a burr or abradersurface. The flute shape and geometry can be limited since it isdictated by the machining process, and burr size and shape limitationsmay direct usage toward more coarse bone removal applications. Further,when operated in a rotational or oscillatory mode, the cutting edgesadapted for coarse bone removal may have a kickback effect as the flutesfirst make contact with bone, which is aggravated by rapid dulling ofthe machined cutting edges.

Therefore, the need exists for arthroscopic burrs and/or shavers thatcan operate to cut and remove bone without the release of fracturedparticles and micro-particles into the treatment site. Further, there isa need for burrs/cutters that do not wear rapidly and that can havecutting edges not limited by metal machining techniques.

SUMMARY OF THE INVENTION

The present invention provides a high-speed rotating cutter or burr thatis fabricated entirely of a ceramic material. In one variation, theceramic is a molded monolith with sharp cutting edges and is adapted tobe motor driven at speeds ranging from 3,000 rpm to 20,000 rpm. Theceramic cutting member is coupled to an elongate inner sleeve that isconfigured to rotate within a metal, ceramic or composite outer sleeve.The ceramic material is exceptionally hard and durable and will notfracture and thus not leave foreign particles in a treatment site. Inone aspect, the ceramic has a hardness of at least 8 GPa (kg/mm²) and afracture toughness of at least 2 MPam^(1/2). The “hardness” value ismeasured on a Vickers scale and “fracture toughness” is measured inMPam^(1/2). Fracture toughness refers to a property which describes theability of a material containing a flaw to resist further fracture andexpresses a material's resistance to such fracture. In another aspect,it has been found that materials suitable for the cutting member of theinvention have a certain hardness-to-fracture toughness ratio, which isa ratio of at least 0.5 to 1.

While the cutting assembly and ceramic cutting member of the inventionhave been designed for arthroscopic procedures, such devices can befabricated in various cross-sections and lengths and can be use in otherprocedures for cutting bone, cartilage and soft tissue such as in ENTprocedures, spine and disc procedures and plastic surgeries.

In a first specific aspect, the present invention provides a medicaldevice includes an elongated sleeve having a longitudinal axis, aproximal end and a distal end. A cutting member extends distally fromthe distal end of the elongated sleeve, and has sharp cutting edges. Thecutting head is formed from a wear-resistant ceramic material, and amotor coupled to the proximal end of elongated sleeve rotates thecutting member. The cutter may be engaged against bone and rotated tocut bone tissue without leaving any foreign particles in the site.

The wear-resistant ceramic material may comprise any one or combinationof (1) zirconia, (2) a material selected from the group ofyttria-stabilized zirconia, magnesia-stabilized zirconia and zirconiatoughened alumina, or (3) silicon nitride. The cutting member typicallyhas from 2 to 100 cutting edges, a cylindrical periphery, and is usuallyrounded in the distal direction. The cutting member will typically havediameter ranging from 2 mm to 10 mm, and the cutting edges willtypically extend over an axial length ranging between 1 mm and 10 mm.The cutting edges may be any one of helical, angled or straight relativeto said axis, and flutes between the cutting edges usually have a depthranging from 0.10 mm to 2.5 mm. An aspiration tube may be configured toconnect to a negative pressure source, where the cutting member has atleast one window in a side thereof which opens to a hollow interior. Inthese embodiments, the hollow interior is open to a central passage ofthe elongated member which is connected to the aspiration tube.

In a further aspect, the present invention provides a medical device fortreating bone including an elongated shaft having a longitudinal axis, aproximal end, and a distal end. A monolithic cutting member fabricatedof a material having a hardness of at least 8 GPa (kg/mm²) is coupled tothe distal end of the elongated shaft, and a motor is operativelyconnected to the proximal end of the shaft, said motor being configuredto rotate the shaft at at least 3,000 rpm.

The material usually has a fracture toughness of at least 2 MPam^(1/2),and further usually has a coefficient of thermal expansion of less than10 (1×10⁶/° C.). The material typically comprises a ceramic selectedfrom the group of yttria-stabilized zirconia, magnesia-stabilizedzirconia, ceria-stabilized zirconia, zirconia toughened alumina andsilicon nitride, and the cutting member typically has a cylindricalperiphery and an at least partly rounded periphery in an axialdirection.

In a still further aspect, the present invention provides a medicaldevice for treating bone comprising a monolithic cutting memberfabricated of a material having a hardness-to-fracture toughness ratioof at least 0.5:1, usually at least 0.8:1, and often at least 1:1.

In yet another aspect, the present invention provides a medical devicefor cutting tissue including a motor-driven shaft having a longitudinalaxis, a proximal end, a distal end, and a lumen extending therebetween.A rotatable cutting member is fabricated entirely of a ceramic materialand is operatively coupled to the distal end of the motor-driven shaft.At least one window in the cutting member communicates with the lumen inthe shaft, and a negative pressure source is in communication with thelumen to remove cut tissue from an operative site.

The ceramic material typically has a hardness of at least 8 GPa (kg/mm²)and a fracture toughness of at least 2 MPam^(1/2). Additionally, theceramic material will usually have a coefficient of thermal expansion ofless than 10 (1×10⁶/° C.). Exemplary ceramic materials are selected fromthe group consisting of yttria-stabilized zirconia, magnesia-stabilizedzirconia, ceria-stabilized zirconia, zirconia toughened alumina andsilicon nitride, and the cutting member usually has cutting edges wherethe at least one window is proximate to the cutting edges, and the atleast one window is in at least one flute between the cutting edges.

In another aspect, the present invention provides a method forpreventing foreign particle induced inflammation at a bone treatmentsite. A rotatable cutter fabricated of a ceramic material having ahardness of at least 8 GPa (kg/mm²) and a fracture toughness of at least2 MPam^(1/2), is engaged against bone and rotated to cut bone tissuewithout leaving any foreign particles in the site.

The ceramic material is usually selected from the group consisting ofyttria-stabilized zirconia, magnesia-stabilized zirconia,ceria-stabilized zirconia, zirconia toughened alumina and siliconnitride, and the cutter is typically rotated at 10,000 rpm or greater.Cut bone tissue is removed from the bone treatment site through achannel in the cutter, typically by aspirating the cut bone tissuethrough the channel.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It should be appreciated that thedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting in scope.

FIG. 1 is a perspective view of a disposable arthroscopic cutter or burrassembly with a ceramic cutting member carried at the distal end of arotatable inner sleeve with a window in the cutting member proximal tothe cutting edges of the burr.

FIG. 2 is an enlarged perspective view of the ceramic cutting member ofthe arthroscopic cutter or burr assembly of FIG. 1.

FIG. 3 is a perspective view of a handle body with a motor drive unit towhich the burr assembly of FIG. 1 can be coupled, with the handle bodyincluding an LCD screen for displaying operating parameters of deviceduring use together with a joystick and mode control actuators on thehandle.

FIG. 4 is an enlarged perspective view of the ceramic cutting membershowing a manner of coupling the cutter to a distal end of the innersleeve of the burr assembly.

FIG. 5A is a cross-sectional view of a cutting assembly similar to thatof FIG. 2 taken along line 5A-5A showing the close tolerance betweensharp cutting edges of a window in a ceramic cutting member and sharplateral edges of the outer sleeve which provides a scissor-like cuttingeffect in soft tissue.

FIG. 5B is a cross-sectional view of the cutting assembly of FIG. 5Awith the ceramic cutting member in a different rotational position thanin FIG. 5A.

FIG. 6 is a perspective view of another ceramic cutting member carriedat the distal end of an inner sleeve with a somewhat rounded distal noseand deeper flutes than the cutting member of FIGS. 2 and 4, and withaspiration openings or ports formed in the flutes.

FIG. 7 is a perspective view of another ceramic cutting member withcutting edges that extend around a distal nose of the cutter togetherwith an aspiration window in the shaft portion and aspiration openingsin the flutes.

FIG. 8 is a perspective view of a ceramic housing carried at the distalend of the outer sleeve.

FIG. 9A is a side cut-away view of a ceramic cutting member and shaftillustrating an aspiration pathway in the assembly.

FIG. 9B is a cut-away view of an alternative working end and ceramiccutting member illustrating multiple aspiration pathways in theassembly.

FIG. 9C is a cut-away view of an alternative working end and ceramiccutting member illustrating both inflow and aspiration pathways in theassembly.

FIG. 9D is a cut-away view of another variation of working end andceramic cutting member illustrating both inflow and aspiration pathwaysin the assembly.

FIG. 10 is a perspective cut-away view of ceramic housing carried by anouter sleeve illustrating an aspiration or inflow pathway.

FIG. 11 is a perspective of a variation of a ceramic cutting memberillustrating with multiple abrading teeth.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to bone cutting and removal devices andrelated methods of use. Several variations of the invention will now bedescribed to provide an overall understanding of the principles of theform, function and methods of use of the devices disclosed herein. Ingeneral, the present disclosure provides for an arthroscopic cutter orburr assembly for cutting or abrading bone that is disposable and isconfigured for detachable coupling to a non-disposable handle and motordrive component. This description of the general principles of thisinvention is not meant to limit the inventive concepts in the appendedclaims.

In general, the present invention provides a high-speed rotating ceramiccutter or burr that is configured for use in many arthroscopic surgicalapplications, including but not limited to treating bone in shoulders,knees, hips, wrists, ankles and the spine. More in particular, thedevice includes a cutting member that is fabricated entirely of aceramic material that is extremely hard and durable, as described indetail below. A motor drive is operatively coupled to the ceramic cutterto rotate the burr edges at speeds ranging from 3,000 rpm to 20,000 rpm.

In one variation shown in FIGS. 1-2, an arthroscopic cutter or burrassembly 100 is provided for cutting and removing hard tissue, whichoperates in a manner similar to commercially available metals shaversand burrs. FIG. 1 shows disposable burr assembly 100 that is adapted fordetachable coupling to a handle 104 and motor drive unit 105 therein asshown in FIG. 3.

The cutter assembly 100 has a shaft 110 extending along longitudinalaxis 115 that comprises an outer sleeve 120 and an inner sleeve 122rotatably disposed therein with the inner sleeve 122 carrying a distalceramic cutting member 125. The shaft 110 extends from a proximal hubassembly 128 wherein the outer sleeve 120 is coupled in a fixed mannerto an outer hub 140A which can be an injection molded plastic, forexample, with the outer sleeve 120 insert molded therein. The innersleeve 122 is coupled to an inner hub 140B (phantom view) that isconfigured for coupling to the motor drive unit 105 (FIG. 3). The outerand inner sleeves 120 ands 122 typically can be a thin wall stainlesssteel tube, but other materials can be used such as ceramics, metals,plastics or combinations thereof.

Referring to FIG. 2, the outer sleeve 120 extends to distal sleeveregion 142 that has an open end and cut-out 144 that is adapted toexpose a window 145 in the ceramic cutting member 125 during a portionof the inner sleeve's rotation. Referring to FIGS. 1 and 3, the proximalhub 128 of the burr assembly 100 is configured with a J-lock, snap-fitfeature, screw thread or other suitable feature for detachably lockingthe hub assembly 128 into the handle 104. As can be seen in FIG. 1, theouter hub 140A includes a projecting key 146 that is adapted to matewith a receiving J-lock slot 148 in the handle 104 (see FIG. 3).

In FIG. 3, it can be seen that the handle 104 is operatively coupled byelectrical cable 152 to a controller 155 which controls the motor driveunit 105. Actuator buttons 156 a, 156 b or 156 c on the handle 104 canbe used to select operating modes, such as various rotational modes forthe ceramic cutting member. In one variation, a joystick 158 be movedforward and backward to adjust the rotational speed of the ceramiccutting member 125. The rotational speed of the cutter can continuouslyadjustable, or can be adjusted in increments up to 20,000 rpm. FIG. 3further shows that negative pressure source 160 is coupled to aspirationtubing 162 which communicates with a flow channel in the handle 104 andlumen 165 in inner sleeve 122 which extends to window 145 in the ceramiccutting member 125 (FIG. 2).

Now referring to FIGS. 2 and 4, the cutting member 125 comprises aceramic body or monolith that is fabricated entirely of a technicalceramic material that has a very high hardness rating and a highfracture toughness rating, where “hardness” is measured on a Vickersscale and “fracture toughness” is measured in MPam^(1/2). Fracturetoughness refers to a property which describes the ability of a materialcontaining a flaw or crack to resist further fracture and expresses amaterial's resistance to brittle fracture. The occurrence of flaws isnot completely avoidable in the fabrication and processing of anycomponents.

The authors evaluated technical ceramic materials and tested prototypesto determine which ceramics are best suited for the non-metal cuttingmember 125. When comparing the material hardness of the ceramic cuttersof the invention to prior art metal cutters, it can easily be understoodwhy typical stainless steel bone burrs are not optimal. Types 304 and316 stainless steel have hardness ratings of 1.7 and 2.1, respectively,which is low and a fracture toughness ratings of 228 and 278,respectively, which is very high. Human bone has a hardness rating of0.8, so a stainless steel cutter is only about 2.5 times harder thanbone. The high fracture toughness of stainless steel provides ductilebehavior which results in rapid cleaving and wear on sharp edges of astainless steel cutting member. In contrast, technical ceramic materialshave a hardness ranging from approximately 10 to 15, which is five tosix times greater than stainless steel and which is 10 to 15 timesharder than cortical bone. As a result, the sharp cutting edges of aceramic remain sharp and will not become dull when cutting bone. Thefracture toughness of suitable ceramics ranges from about 5 to 13 whichis sufficient to prevent any fracturing or chipping of the ceramiccutting edges. The authors determined that a hardness-to-fracturetoughness ratio (“hardness-toughness ratio”) is a useful term forcharacterizing ceramic materials that are suitable for the invention ascan be understood form the Chart A below, which lists hardness andfracture toughness of cortical bone, a 304 stainless steel, and severaltechnical ceramic materials.

CHART A Ratio Fracture Hardness to Hardness Toughness Fracture (GPa)(MPam^(1/2)) Toughness Cortical bone 0.8 12  .07:1 Stainless steel 3042.1 228  .01:1 Yttria-stabilized zirconia (YTZP) YTZP 2000 (SuperiorTechnical 12.5 10 1.25:1 Ceramics) YTZP 4000 (Superior Technical 12.5 101.25:1 Ceramics) YTZP (CoorsTek) 13.0 13 1.00:1 Magnesia stabilizedzirconia (MSZ) Dura-Z ® (Superior Technical 12.0 11 1.09:1 Ceramics) MSZ200 (CoorsTek) 11.7 12 0.98:1 Zirconia toughened alumina (ZTA) YTA-14(Superior Technical 14.0 5 2.80:1 Ceramics) ZTA (CoorsTek) 14.8 6 2.47:1Ceria stabilized zirconia CSZ (Superior Technical 11.7 12 0.98:1Ceramics) Silicon Nitride SiN (Superior Technical 15.0 6 2.50:1Ceramics)

As can be seen in Chart A, the hardness-toughness ratio for the listedceramic materials ranges from 98× to 250× greater than thehardness-toughness ratio for stainless steel 304. In one aspect of theinvention, a ceramic cutter for cutting hard tissue is provided that hasa hardness-toughness ratio of at least 0.5:1, 0.8:1 or 1:1.

In one variation, the ceramic cutting member 125 is a form of zirconia.Zirconia-based ceramics have been widely used in dentistry and suchmaterials were derived from structural ceramics used in aerospace andmilitary armor. Such ceramics were modified to meet the additionalrequirements of biocompatibility and are doped with stabilizers toachieve high strength and fracture toughness. The types of ceramics usedin the current invention have been used in dental implants, andtechnical details of such zirconia-based ceramics can be found inVolpato, et al., “Application of Zirconia in Dentistry: Biological,Mechanical and Optical Considerations”, Chapter 17 in Advances inCeramics—Electric and Magnetic Ceramics, Bioceramics, Ceramics andEnvironment (2011).

In one variation, the ceramic cutting member 125 is fabricated of anyttria-stabilized zirconia as is known in the field of technicalceramics, and can be provided by CoorsTek Inc., 16000 Table MountainPkwy., Golden, Colo. 80403 or Superior Technical Ceramics Corp., 600Industrial Park Rd., St. Albans City, Vt. 05478. Other technicalceramics that may be used may be selected from the group consisting ofmagnesia-stabilized zirconia, ceria-stabilized zirconia, zirconiatoughened alumina and silicon nitride. In general, in one aspect of theinvention, the monolithic ceramic cutting member 125 has a hardnessrating of at least 8 GPa (kg/mm²). In another aspect of the invention,the ceramic cutting member 125 has a fracture toughness of at least 24MPam^(1/2).

The fabrication of such ceramics or monoblock components are known inthe art of technical ceramics, but have not been used in the field ofarthroscopic or endoscopic cutting or resecting devices. Ceramic partfabrication includes molding, sintering and then heating the molded partat high temperatures over precise time intervals to transform acompressed ceramic powder into a ceramic monoblock which can provide thehardness range and fracture toughness range as described above. In onevariation, the molded ceramic member part can have additionalstrengthening through hot isostatic pressing of the part. Following theceramic fabrication process, a subsequent grinding process optionallymay be used to sharpen the cutting edges 175 of the burr (see FIGS. 2and 4).

In FIG. 4, it can be seen that in one variation, the proximal shaftportion 176 of cutting member 125 includes projecting elements 177 whichare engaged by receiving openings 178 in a stainless steel split collar180 shown in phantom view. The split collar 180 can be attached aroundthe shaft portion 176 and projecting elements 177 and then laser weldedalong weld line 182. Thereafter, proximal end 184 of collar 180 can belaser welded to the distal end 186 of stainless steel inner sleeve 122to mechanically couple the ceramic body 125 to the metal inner sleeve122. In another aspect of the invention, the ceramic material isselected to have a coefficient of thermal expansion between is less than10 (1×10⁶/° C.) which can be close enough to the coefficient of thermalexpansion of the metal sleeve 122 so that thermal stresses will bereduced in the mechanical coupling of the ceramic member 125 and sleeve122 as just described. In another variation, a ceramic cutting membercan be coupled to metal sleeve 122 by brazing, adhesives, threads or acombination thereof.

Referring to FIGS. 1 and 4, the ceramic cutting member 125 has window145 therein which can extend over a radial angle of about 10° to 90° ofthe cutting member's shaft. In the variation of FIG. 1, the window ispositioned proximally to the cutting edges 175, but in other variations,one or more windows or openings can be provided and such openings canextend in the flutes 190 (see FIG. 6) intermediate the cutting edges 175or around a rounded distal nose of the ceramic cutting member 125. Thelength L of window 145 can range from 2 mm to 10 mm depending on thediameter and design of the ceramic member 125, with a width W of 1 mm to10 mm.

FIGS. 1 and 4 shows the ceramic burr or cutting member 125 with aplurality of sharp cutting edges 175 which can extend helically,axially, longitudinally or in a cross-hatched configuration around thecutting member, or any combination thereof. The number of cutting edges175 ands intermediate flutes 190 can range from 2 to 100 with a flutedepth ranging from 0.10 mm to 2.5 mm. In the variation shown in FIGS. 2and 4, the outer surface or periphery of the cutting edges 175 iscylindrical, but such a surface or periphery can be angled relative toaxis 115 or rounded as shown in FIGS. 6 and 7. The axial length AL ofthe cutting edges can range between 1 mm and 10 mm. While the cuttingedges 175 as depicted in FIG. 4 are configured for optimal bone cuttingor abrading in a single direction of rotation, it should be appreciatedthe that the controller 155 and motor drive 105 can be adapted to rotatethe ceramic cutting member 125 in either rotational direction, oroscillate the cutting member back and forth in opposing rotationaldirections.

FIGS. 5A-5B illustrate a sectional view of the window 145 and shaftportion 176 of a ceramic cutting member 125′ that is very similar to theceramic member 125 of FIGS. 2 and 4. In this variation, the ceramiccutting member has window 145 with one or both lateral sides configuredwith sharp cutting edges 202 a and 202 b which are adapted to resecttissue when rotated or oscillated within close proximity, or inscissor-like contact with, the lateral edges 204 a and 204 b of thesleeve walls in the cut-out portion 144 of the distal end of outersleeve 120 (see FIG. 2). Thus, in general, the sharp edges of window 145can function as a cutter or shaver for resecting soft tissue rather thanhard tissue or bone. In this variation, there is effectively no open gapG between the sharp edges 202 a and 202 b of the ceramic cutting member125′ and the sharp lateral edges 204 a, 204 b of the sleeve 120. Inanother variation, the gap G between the window cutting edges 202 a, 202b and the sleeve edges 204 a, 204 b is less than about 0.020″, or lessthan 0.010″.

FIG. 6 illustrates another variation of ceramic cutting member 225coupled to an inner sleeve 122 in phantom view. The ceramic cuttingmember again has a plurality of sharp cutting edges 175 and flutes 190therebetween. The outer sleeve 120 and its distal opening and cut-outshape 144 are also shown in phantom view. In this variation, a pluralityof windows or opening 245 are formed within the flutes 190 andcommunicate with the interior aspiration channel 165 in the ceramicmember as described previously.

FIG. 7 illustrates another variation of ceramic cutting member 250coupled to an inner sleeve 122 (phantom view) with the outer sleeve notshown. The ceramic cutting member 250 is very similar to the ceramiccutter 125 of FIGS. 1, 2 and 4, and again has a plurality of sharpcutting edges 175 and flutes 190 therebetween. In this variation, aplurality of windows or opening 255 are formed in the flutes 190intermediate the cutting edges 175 and another window 145 is provided ina shaft portion 176 of ceramic member 225 as described previously. Theopenings 255 and window 145 communicate with the interior aspirationchannel 165 in the ceramic member as described above.

It can be understood that the ceramic cutting members can eliminate thepossibility of leaving metal particles in a treatment site. In oneaspect of the invention, a method of preventing foreign particle inducedinflammation in a bone treatment site comprises providing a rotatablecutter fabricated of a ceramic material having a hardness of at least 8GPa (kg/mm²) and/or a fracture toughness of at least 2 MPam^(1/2) androtating the cutter to cut bone without leaving any foreign particles inthe treatment site. The method includes removing the cut bone tissuefrom the treatment site through an aspiration channel in a cuttingassembly.

FIG. 8 illustrates variation of an outer sleeve assembly with therotating ceramic cutter and inner sleeve not shown. In the previousvariations, such as in FIGS. 1, 2 and 6, shaft portion 176 of theceramic cutter 125 rotates in a metal outer sleeve 120. FIG. 8illustrates another variation in which a ceramic cutter (not shown)would rotate in a ceramic housing 280. In this variation, the shaft or aceramic cutter would thus rotate is a similar ceramic body which may beadvantageous when operating a ceramic cutter at high rotational speeds.As can be seen in FIG. 8, a metal distal metal housing 282 is welded tothe outer sleeve 120 along weld line 288. The distal metal housing 282is shaped to support and provide strength to the inner ceramic housing282.

FIGS. 9A-9D illustrate variations of cutter assemblies 400A-400D thatinclude ceramic cutters 405A-405C with various fluid inflow and fluidoutflow channels that can be incorporated into the assembly. FIG. 9Aillustrates a cutter assembly 400A with a monoblock ceramic cutter 405Acoupled to inner sleeve 412 that rotates in outer sleeve 420. The outersleeve 420 can be a ceramic, metal, polymer or combination thereof andincludes a plurality of three to ten collar elements 422 in the bore 425in which the inner sleeve 412 and ceramic cutter rotate. The negativepressure source 160 described above is connected to bore 425 to aspiratefluid and tissue debris through the gaps (indicated by arrows) betweenthe collar elements 422 outwardly to a collection reservoir.

FIG. 9B illustrates another variation of cutter assembly 400B that issimilar to the version of FIG. 9A except that the ceramic cutting member405B has an interior flow channel 440 that communicates with openings444 in the surface of the cutting member. In this variation, thenegative pressure source 160 is connected to flow channel 440 in theceramic cutter 405B to thus aspirate fluid and tissue debris through thecutter (indicated by arrows) as well as through bore 425 in outer sleeve420. FIG. 9C illustrates another variation of cutter assembly 400C thatis similar to that of FIG. 9B except that a fluid inflow channel 448 isprovided in a hypotube 450 coupled to the exterior of outer sleeve 420.The fluid inflow can be low pressure, high pressure and/or pulsed toinfuse the treatment site with fluid.

FIG. 9D illustrates a variation of cutter assembly 400D that is similarto that of FIG. 9B except that ceramic cutting member 405D has aninterior flow channel 460 that communicates with openings 464 and afluid inflow source is coupled thereto for providing fluid inflowsthrough the ceramic cutting member 405D as indicated by arrows. Thefluid outflows are provided through bore 425 in outer sleeve 420 asdescribed previously.

FIG. 10 illustrates another variation of an outer sleeve assembly 465without showing the rotating ceramic cutter. The variation of FIG. 10 issimilar to that of FIG. 8 and includes a ceramic housing 470 carried inan outer metal housing 472 coupled to outer sleeve 475. In thisvariation, the ceramic housing 470 has a flow channel 477 and ports 480formed therein that communicate with a negative pressure source 160 toaspirate fluid as indicated by the arrows in FIG. 10. The channel 477extends proximally though a flow passageway 482 in the wall of outersleeve 475. In one variation, the ceramic housing 470 can comprise aresilient ceramic with wall portion 484 molded so as to be biasedagainst a rotating ceramic cutter. In another variation, fluid inflowscould be provided through flow channel 477 and ports 480.

FIG. 11 illustrates another variation of a ceramic cutting member 500that has a plurality of abrading teeth 502, ports 504 and an interiorflow channel 505 which can be fabricated as described above by a ceramicmolding process. A complex part as shown in FIG. 11 would be expensiveto fabricate from a metal, such as stainless steel.

In another embodiment (not shown) a cutting member can be fabricated ofcorundum. Corundum is a crystalline form of aluminum oxide which mayhave various colors, and which generally is referred to as sapphire. Theterms “corundum” and “sapphire” may be used interchangeably herein torefer to the crystalline form of aluminum oxide. A monolithic,monocrystal cutting member could be made from a sapphire and fallswithin the scope of the invention, and would be most suitable for simplecutting elements as fabrication costs would be high for any complexshapes. Similarly, silica and silica borate and other forms of glassfall within the scope of the invention.

Now referring to FIG. 3, the handle 104 can be a conventionalnon-disposable component and includes a control panel 260 that isadapted to allow simplified manual (thumb) control of multiple functionsof the device together with an LCD display 265 that can provide thephysician with visual information about operating parameters.

In one variation, the joystick 158 can be used to actuate the motordrive and also to control its speed and direction of rotation. In avariation, the joystick 158 is adapted for movement in four directionsand also can be depressed downwardly to actuate a function. In onevariation, the joystick 158 can be pushed downward to activate the motordrive and released to de-activate the motor drive. The joystick 158 canbe moved forward and backward relative to the axis of handle 104 toeither increase or decrease the speed of the motor. In such a variation,movement of joystick 158 to the left or to the right can increase ordecrease fluid inflow/outflow rates from a fluid management systemassociated with an arthroscopic procedure.

The control panel 260 further includes push buttons 156 a, 156 b and 156c that can be used to select various operational modes, such asselection of forward (clockwise) rotating mode, selection of backward(counter-clockwise) rotating mode, selection of intermittent forward orbackward rotating mode, selection of oscillating mode, selection oflevel of aspiration through an extraction channel of the device,selection of inflows such as a flush mode and the like.

In another embodiment, a cutting system as shown in FIGS. 1, 3, 4, 6 and8A-8D can have a controller that is operatively coupled to both themotor 105 and the negative pressure source 160 (see FIG. 3) to controlrotational speed of the ceramic cutting member as well as to control thenegative pressure level. In a variation, the controller includes analgorithm that modulates negative pressure and thus fluid outflows inresponse to the rotational speed of the ceramic cutting member. Forexample, an algorithm can increase negative pressure and fluid outflowsas the speed of the cutter increases to thereby remove greater volumesof fluid and tissue debris. In one system embodiment, the controller cancontrol a fluid outflow pump and a fluid inflow pump, and the speed ofthe outflow pump (and negative pressure) can be modulated in response tothe rotational speed of the cutter. In this system variation, thecontroller also can control the inflow pump to increase fluid inflowsinto a treatment site in response to increases in the rotational speedof the cutter, or in response to the increase in speed of the outflowpump.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method of preventing metal particle inducedinflammation in a joint treatment site comprising; providing a cuttingdevice comprising (i) an inner sleeve that carries a distal rotatablecutter fabricated from a ceramic material having a hardness of at least8 Gpa (kg/mm²) and a fracture toughness of at least 2 M Pam^(1/2), thecutter having a window with a pair of opposed lateral sides each havinga cutting edge, wherein said window opens to a central channel thereinthat communicates with a negative pressure source, and (ii) an outersleeve fabricated from a metal having a distal cut-out portion withlateral edges, wherein said distal cut-out portion is rotationallyaligned with cutter window; rotating the inner sleeve within the outersleeve to pass the cutting edges of the window past the lateral edges ofthe distal cut-out portion to cut tissue therebetween, wherein a gapbetween the cutting edges of the window and the lateral edges of thecut-out portion of the metal outer sleeve as the cutting edges pass thelateral edges is less than 0.020″; and activating the negative pressuresource to extract tissue chips through the window and the centralchannel and into the collection reservoir.
 2. The method of claim 1,wherein the ceramic material is selected from the group consisting ofyttria-stabilized zirconia, magnesia-stabilized zirconia,ceria-stabilized zirconia, zirconia toughened alumina and siliconnitride.
 3. The method of claim 1, wherein the cutter is rotated at3,000 rpm or greater.
 4. The method of claim 1, further comprisingengaging the window with cutting edges against soft tissue whilerotating the inner sleeve to cut soft tissue.
 5. The method of claim 4,wherein the cutting device further comprises sharp cutting edges formeddistally of the window, further comprising engaging the sharp cuttingedges against bone while rotating the inner sleeve to remove bonetissue.
 6. The method of claim 5, wherein the cutter is rotated at10,000 rpm or greater.